The first milestone discoveries of a true detection of the IGrM in the two galaxy groups NGC 2300 [1]} (see Fig.REF ) and HCG 62 [2]} done with ROSAT pointed to a surprisingly low abundance of the plasma of 0.09 Solar for NGC 2300 and 0.22 Solar for HCG 62, assuming the RS thermal plasma model [3]}. The entire detectable extent of the emission was fitted in a single aperture (25\(^\prime \)  for NGC 2300 and 18\(^\prime \)  for HCG 62, in the case of the analysis of NGC 2300 excluding the emission around the central galaxy itself).
The ROSAT observation of NGC 5044 [4]} made it possible to measure spatially resolved temperatures and abundances, with super-Solar abundances in the inner 6\(^{\prime }\)  and beyond that radius consistent with a uniform distribution of 1.2 Solar. Very low abundance, \(<0.12\) , was reported in the NGC 4261 group from a fit with a RS model to a spectrum extracted from 40\(^{\prime }\)  [5]}. In the first sample of HCGs [6]} a solid detection of extended emission in 3 of them (the already mentioned HCG 62, HCG 92 and HCG 97) and a possible detection in another 3, were all well fitted by a RS model with very low metal abundances. Additional ROSAT observations allowed spatially resolved measurements for NGC 2300 confirming the low abundance, less than 0.16 Solar [7]}. In a more complete survey of 85 HCGs with either deeper pointed (in 32 cases) or survey ROSAT PSPC observations, extended emission from an IGrM was detected in 22 of them, including in the group emission also the emission spatially located on the dominant central elliptical [8]}. The metallicity derived for the 12 spectra of enough quality within an aperture of 200 kpc (in their cosmology) all pointed to a low abundance with a weighted mean of 0.27 Solar. Interestingly enough [8]} commented to treat these results with caution because the inferred low metal abundances rely heavily on the isothermal assumption: when temperature variations in the gas are taken into account, metallicities several times higher can be inferred. [10]} extended the search for ROSAT observation of galaxy groups beyond HCGs with other optical catalogues in a sample of additional 14 groups finding emission from 4 of them and extending the census of the IGrM to 25 of the 48 groups analyzed at that time. Some conclusions were starting to be made, with the general lower abundance of the IGrM with respect to the ICM, despite the more equal share between gas and stellar mass, possibly suggesting that the IGrM may be largely primordial.
